The subscriber loop which connects the customer premises equipment (CPE) to the central office (CO) can be affected by a wide range of impairments, including bridge taps, mixed wire gauges, bad splices, split pairs, untwisted drop cables, radio-frequency interference (RFI), and cross-talk. Although wire gauge of the loop and loop length are generally not considered actual impairments, they also have a huge impact on xDSL (i.e. ADSL, VDSL, etc.) transmission performance. Conventional methods for evaluating and qualifying a subscriber loop include the use of xDSL test units available on the market that are capable of performing such measurements. In addition, these test units are often combined with a “golden” modem plug-in module that emulates a real xDSL modem of a certain type, such as ADSL, in order to estimate the real bit rate instead of only the theoretical channel capacity. However, this approach requires sending a technician to the customer premises, which is very expensive. Meanwhile, conventional single-ended loop testing (SELT) can be used to extract information about the transmission environment and network topology in a DSL system by performing reflective measurements remotely at the CO or CPE terminal, without the need to dispatch a technician.
Regarding the problem of mixed wire gauges, in North America, the size of a copper wire is measured in American Wire Gauge (AWG) and represents the “thickness” or diameter of the copper wire. Historically, a wire gauge was determined by how much its diameter could be reduced when stepping through the wire die that was used to extrude it. So, for example, going from an 11 AWG to 12 AWG would reduce the wire diameter by a factor of about 0.89. This seems to be the limit and is still the case today.
Conventional gauge detection techniques include those that based on SELT measurements. However, a problem exists in that such techniques are interdependent on determining other features of the loop such as loop length estimation, bridge-tap location and termination detection, etc. Accordingly, a need for addressing potential problems arising from such interdependence exists.